Recently because of the high cost of oil, gas and electricity the use of bio-mass materials such as wood chips, bark, sawdust and the like for heating and generation of power is being seriously considered as a supplement to and even a replacement for oil, gas and electricity. Such apparatus as is available generates so much air borne ash that it is objectionable from the standpoint of pollution and is rapidly rendered ineffective by deposits of tar and resin on the grates and in the flues. The apparatus of this invention is designed to convert bio-mass materials such as wood, wood chips, sawdust, bark and the like to a combustible gas without generation of pollutants either in the form of solid particles such as ash or condensates such as tars and resins and to obtain a maximum BTU value per unit of wood consumed.